How do Nichirin blade replicas achieve their color variations?
Updated Feb 2026
In the Demon Slayer series, Nichirin blades change color based on the wielder — and the replica versions achieve this through a combination of differential polishing, heat treatment application, and blade coating techniques applied after forging. Unlike standard katana replicas where the steel is left in a uniform polish or black finish, Nichirin replicas involve additional finishing steps to produce colors like flame orange, thunder yellow, or Tanjiro's signature black. These finishes are applied to the surface layer of the carbon steel blade and are designed for display stability rather than heavy handling. Collectors should store Nichirin replicas away from high humidity and direct sunlight to preserve the color treatment over time, and should apply a thin layer of blade oil every few months to protect the underlying carbon steel from oxidation beneath the finish.